Robin Williams is a great idea for Bombadil as is Stewart for Saruman. Gellar is a good choice for Eowyn too. Would they do CGI on dwarves, trolls, and ents too? That could be key in casting. The problem with hobbits is I don't think they looked like midgets(I write this so not to confuse the modern term dwarf and the mythological dwarf) Little people, as I will now call them, could play dwarves. Ents and Trolls obviously pose a problem since their heights are roughly 14 and 12 feet respectively.

Once again Robin Williams is the hands down choice for Bombadil. If anybody can capture this enigma, it is the diverse talent of Williams.

Jon